1. Field of the Invention
The present invention relates to x-ray imaging, more particularly, to backscatter x-ray imaging of soft body tissue.
2. Description of the Related Art
X-ray imaging has been done by conventional transmission x-rays for many years. A major limitation to the spatial resolution of transmission x-ray systems is the scattering of the primary beam as it penetrates the breast. The fraction of scattered x-rays to the non-scattered x-rays (the only useful rays in the image) can be more than a factor of 2 for a beam of 30 keV peak at a breast thickness of approximately 5 cm, resulting in a loss of contrast and spatial resolution.
Film imaging has now been largely replaced by digital imaging. This more convenient mode does not produce better spatial resolution but is superior in allowing convenient transmission of the images and manipulation to better evaluate the images.
Still more recent is the development of three-dimensional (3D) systems for breast imaging. These systems use digital tomography/laminography algorithms that produce 3D images that appear at the present time to be better able to detect small cancers of the breast. 3D images are produced by producing approximately 15 to 20 transmission images of a breast from different angles, combining the images, and using an algorithm that chooses selected pixels at a given depth that appear in each of the transmission images and blurring all the other pixels. The resulting blurred 3D image is refined by a series of “maximum likelihood” enhancements that reduce the blurring.
Thermal (infrared) imaging of the breast has a long history. It has recently been proposed to use nano-particles that have been tagged to locate tumor tissue together with external magnetic field excitation to locally heat suspect areas in the breast for imaging and treatment.
The use of backscatter x-ray systems for the inspection of personnel for security purposes is now common. These systems operate at very low exposure levels and are limited to an exposure of 10 micro-Roentgens (μR) by government regulation. The current system will provide more than 1000 times greater x-ray flux to the patient than the security systems, providing image quality never seen before in soft tissue or the lung.